Justification:
This species has been uplisted to Near Threatened because the global population decline is likely to approach 30% in three generations (23 years). If the decline is found to be larger then the species could qualify for further uplisting; it almost meets the requirements for listing as threatened under criteria A2b+3b+4b.

The species ranges from Baja California (Mexico) up the Pacific coast of the U.S.A. and Canada, through Alaska to the Aleutian Islands (U.S.A.) (del Hoyo et al. 1996). British Columbia (Canada) supports the largest population with approximately 2,700,000 breeding birds; it is estimated that there are approximately 600,000 birds in Alaska, 88,000 in Washington, 500 in Oregon, 131,000 in California and 20,000-40,000 in Baja California on the islands of San Benito, San Geronimo, Asuncion and San Roque (Nettleship 1996).

The total population is estimated to be at least 3,600,000 breeding birds (Nettleship 1996) which equates to approximately 5,400,000 individuals.

Trend Justification: This species has apparently undergone a large and statistically significant decrease over the last 40 years in North America (-96.8% decline over 40 years, equating to a -57.9% decline per decade; data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007, although these surveys cover less than 50% of the species's range in North America). A recent study by Rodway and Lemon (2011) found declines in monitored burrows at several colonies in British Columbia, and estimated a 40% decline in monitored burrows over 20 years between 1989 and 2009 in the largest known breeding population on Triangle Island (part of the Scott Islands). Declines appear to have begun in c.1990, and if the declines on Triangle Island are representative of the whole Scott Islands population then there could have been a total loss of approximately 800,000 birds in the region, or >20% of the world breeding population. Large-scale declines have also been documented on the South Farallon Islands, California (H. Carter in litt. 2013). The overall rate of decline is currently placed in the band 20-29% in three generations (23 years), but confirmation that similar declines are taking place across the whole range would lead to the overall rate of decline being increased.

This species is found offshore and along sea coasts, mostly over the continental shelf to the edge but also beyond into deep ocean. It feeds mostly on crustaceans throughout the year, supplemented by other invertebrates and small larval fish. The start of the breeding season varies greatly with latitude, from November in Baja California to July in Alaska. Birds form colonies from under 500 birds to over one million, usually at high densities on coastal islands with or without trees and nesting on a wide range of habitats. It winters mainly offshore within the breeding range, with southerly populations being relatively sedentary compared to northern individuals which migrate south (del Hoyo et al. 1996).

Introduced predators including rats (Rattus rattus and R. norvegicus), cats, foxes and grazing animals, such as goats represent the most serious threat to colonies (Nettleship 1996, Rodway and Lemon 2011). Raccoons (Procyon lotor) are also a threat on some islands in British Columbia (Rodway and Lemon 2011). Oil pollution represents a significant threat and oil and gas extraction operations may impact negatively on the species through increased pollution and collision with lights (Harfenist 2004). Accidental bycatch in fishing nets is also considered a threat (Harfenist 2004). The species is vulnerable to loss of habitat and disturbance owing to tourism development, recreational and research activities as well as aquaculture and logging operations (Nettleship 1996). The species may be vulnerable to collisions with wind turbines. Losses have also been attributed to increases in numbers of Bald Eagles Haliaeetus leucocephalus, Peregrine Falcon Falco peregrinus and Western Gulls Larus occidentalis in some areas (Nettleship 1996). Fluctuations in the northern Californian populations may be partially explained by anomalous warm-water conditions (Nettleship 1996) which are also thought to be responsible for mass die-offs reported from California to central British Columbia in 2014 (Welch 2015). The species is vulnerable to the effects of climate change, particularly changes in coastal upwelling systems (Wolf et al. 2010).

Conservation and Research Actions UnderwayThe species, its eggs and nests are protected from hunting and collecting in the U.S.A. and Canada under the Migratory Birds Convention Act (Harfenist 2004). In 2002 a rat eradication programme was carried out on Ancapa Island, California. Within one year Cassin's Auklet nests were detected on the island and between 2003 and 2012 a total of 42 nests were discovered (Whitworth et al. 2015). Rat eradications have been carried out in other areas of the species's range, including Langara Island, British Columbia (Regehr et al. 2007).